Existing methods for detection of small RNAs such as small interfering RNAs (siRNAs) and micro RNAs (miRNAs) often involve multiple steps: for example, immobilizing RNA on a filter (Northern blot), hybridization with a specific probe if the small RNA is a single-stranded miRNA, washing steps to remove the probe, and exposure of the filter to a film. Alternatively, small single-stranded RNAs (ssRNAs) such as micro RNAs (miRNAs) can be detected using solution hybridization of a probe to the miRNAs, RNAse treatment and gel electrophoresis to analyze the miRNA/probe product. Detection of miRNA using a DNA array requires fluorescent-labeling of total RNA. Labeling of samples adds complexity and variability to the results. Methods that require DNA amplification are sensitive but need corrections related to efficiency of amplification. These methods are not appropriate for rapid diagnostics or high throughput screening because of the multiple steps involved in the analysis.
Evidence is accumulating that small RNAs such as miRNAs are involved in human disease such as neurological diseases, cardiomyopathies, and cancers (Alvarez-Garcia et al. Development 132:4653-4662 (2005)). Patterns of altered miRNA expression in tissue biopsies may serve as diagnostic markers for these diseases. For example, the use of a reliable quantitative method for detecting the differential expression of certain miRNAs in various tumors would be valuable for diagnosis and treatment of cancer.